Today’s post will help you guys who are taking on a new bike build. As a tech here at J&P Cycles, I’m often asked how long a fork I should purchase? There’s really no way for me to answer that question because it’s something you must decide for yourself. That being said, here’s an explanation of the easiest way I have found to help people arrive at the best answer. 

  • First, we need to mock up the rear wheel we’re going to use with the frame we have.
  • Next — and most important — we’re going to block the front of our chassis up to give us the ride height and “look” that we want. Once this is established, everything else is downhill.
  • We also need to know the radius of the wheel/tire combination we are going to run. For a 16-inch or a 21–inch, we’ll use a radius of 13 inches. For a 19–inch, we’ll use a radius of 12 inches
  • Take a broomstick or mop handle and drop it through the steering neck. Of course, now you’ll need to know use what wheel radius we are running up front in order to get our first dimension point.
  • Measure the radius of the wheel we’re going to use from the broomstick (straight to the floor), and then mark the broomstick at that point. (this mark represents our axle center).
  • Next, measure from the point of the mark to the top of the frame. This gives us the desired fork length.

A stock FXST has a fork length that is very close to 32 inches. If you need a 34-inch length fork, you would need to order a +2 fork. If you need 38-inch fork, then +6 is what you’ll need. If you need a fork shorter than 32 inches, we would select -2 or -4 (depending on what you measure).

OK, we’ve talked about tube type forks, but Springer’s measure slightly differently. According to Paughco, the builder of the highest-quality, largest-volume custom Springer’s available today, the measurement is also from the top tree (top of the steering neck), but the bottom measurement goes to the center of the rear leg pivot. For a Springer, the stock length is considered to be 27 inches. A stock HD late-model Springer is +3 inches (30 inches) for comparison purposes.

As always, our dedicated tech staff is available to answer any of your questions. Reach them via e-mail, phone or chat (to get started, visit the J&P Cycles Customer Service page today).